Sunscreen should be used on your skin if you want to protect yourself from the harmful rays of the sun.
Many chemical fertilizers and pesticides used in agriculture are harmful for health.
Too much TV watching is harmful and wastage of time and energy.
Drinking is harmful to health.
Excessive freedom may spoil the child, whereas no freedom may also prove equally harmful.
Man these days is surrounded by electronics which throw harmful rays.
The vermin are harmful to plants, birds, etc.
Smoking is harmful to health.
That chemical is harmful to your health.
Excess of anything is harmful.
Greed is harmful.